A frame structure used in a wireless LAN in accordance with the related art will be described below.
FIG. 1 illustrates a structure of a frame used in a wireless LAN (IEEE802.11, Wi-Fi).
As shown in FIG. 1, 802.11 medium access control (MAC) frame includes a header.
The MAC header includes a type field 12 and a more fragment field 10. The type field 12 identifies whether a frame body 11 of the MAC frame includes control information (for example, management frame) or data information.
The more fragment field 10 indicates whether a fragment additionally transmitted through the frame body 11 exists. In other words, specific data is divided into a plurality of fragments, and the more fragment field 10 may be set if a fragment to be received still exists.
FIG. 2 illustrates an example of a management frame used in a wireless LAN. The management frame includes various kinds of information in the frame body. Table shown in FIG. 2 indicates a beacon frame included in the frame body of the management frame, a probe request frame, and a probe response frame. The beacon frame, the probe request frame, and the probe response frame are examples of the management frame.
Various parameter sets are defined as shown.
FIG. 3 illustrates components of a management frame body used in a wireless LAN system. The components of the management frame body are comprised of a fixed area and an information element area. Fixed-length mandatory frame body components within the management frame are defined by the fixed area, and variable length mandatory frame body components and optional frame body components are defined by the information element area.
Hereinafter, a related art remote request broker (RRB) will be described.
The RRB which is one of elements of an access point (AP) of a wireless LAN exists in a system management entity (SME) of the AP. The RRB enables communication between APs which exist within a single mobility domain. In other words, communication through a distribution system (DS) is supported between the APs which own the same mobility domain ID by a logical connection structure through the DS. The RRB generates remote request/response frames between a current AP and a next candidate AP or relays messages between them.
Hereinafter, the operation of the related art device will be described.
1. General Configuration of a Wireless LAN (IEEE802.11)
The wireless LAN means a network environment that provides LAN services to a wireless user equipment provided with a wireless LAN card, such as PDA and notebook PC, by using an access point (AP) device corresponding to a hub of a wire LAN. In other words, the wireless LAN may be regarded as a system obtained by replacing a wire section between a hub and a user equipment in an existing Ethernet system with a wireless section between an AP and a network interface card (NIC) such as a wireless LAN card. Since the wireless LAN does not require wiring of a wireless user equipment, it has advantages in that it is easy to rearrange the wireless user equipment and to construct and extend networks, and enables communication during motion. On the other hand, the wireless LAN has disadvantages in that transmission speed is relatively lower than that of the wire LAN, signal quality is unstable in view of properties of a wireless channel, and signal interference may occur.
FIG. 4 illustrates a configuration of a wireless LAN network according to the related art. As shown in FIG. 4, the wireless LAN network is classified into two types depending on whether the network includes AP. The wireless LAN network, which includes the AP, is referred to as an infrastructure network while the wireless LAN network, which does not include the AP, is referred to as an ad-hoc network. A service area provided by one AP is referred to as a basic service area (BSA), and the AP and a wireless user equipment which is connected with the AP are referred to as a basic service set (BSS). A service provided to the wireless user equipment connected with the AP is referred to as a station service (SS). The SS includes a service exchanged between wireless user equipments in the ad-hoc network. As shown, the BSA which is a service area may be overlapped with another BSA. Two or more APs are interworked with one another, so that a wireless user equipment connected with a corresponding AP performs communication with a wireless user equipment connected with another AP. In this case, connection between the respective APs is referred to as a distribution system (DS). A service provided through the DS is referred to as a distribution system service (DSS). Also, an area that can be provided by the DSS is referred to as an extended service area (ESA). All the wireless user equipments and APs which receive the DSS within the ESA are referred to as an extended service set (ESS).
Services prescribed by the IEEE 802.11 standard provide nine lists as shown in Table 1 below.
TABLE 1a) Authenticationb) Associationc) Deauthenticationd) Deassociatione) Distributionf) Integrationg) Privacyh) Reassociationi) MSDU delivery
The authentication service and the deauthentication service relate to user authentication, and the association service, the deassociation service, and the reassociation service relate to access of a wireless user equipment to an AP. The reassociation service is used when the wireless user equipment shifts the BSS within the ESS or the current access status. The distribution service is a conceptional service that a wireless user equipment connected with one AP can perform communication with a wireless user equipment connected with another AP through the DS. The integration service is used for access between IEEE 802.11 LAN and an external LAN regardless of wire LAN or wireless LAN.
Each list of the services depends on setting of the DS. The privacy service relates to security and uses a wired equivalent privacy (WEP) protocol. The MSDU (MAC service data unit) service is used to transmit data of a user. Table 2 shows that the aforementioned service lists are collected and divided into two service categories described above.
TABLE 2DSS (Distribution SystemSS (Station Service)Service)a) Authenticationb) Deauthenticationc) Privacyd) MSDU deliverya) Associationb) Deassociationc) Distributiond) Integratione) Reassociation
The wireless LAN AP performs various functions such as a hub function of a wire LAN, bridge function, home gateway function, automatic fall-back function, and roaming function. The bridge function enables communication between two buildings, which are located far away from each other, using an oriented high gain external antenna. The home gateway function performs access of information communication devices at home to an external network using a wireless LAN AP. The automatic fall-back function serves to allow the AP to lower transmission speed from 11 Mbps to 5.5 Mbps, 2 Mbps, or 1 Mbps if the channel status becomes bad as the distance between the AP and the wireless user equipment becomes more distant. If transmission speed is maintained at 11 Mbps of high speed even in case that the channel status is not good, loss due to retransmission occurs seriously. Accordingly, it is desirable to appropriately lower the transmission speed. The basic roaming function can be performed between the BSSs.
2. Typical Example of Wireless LAN Network
FIG. 5 illustrates a communication environment where coverages of several APs are overlapped with one another. If hand-off is supported within a single ESS as the 802.11 technology is actively used, the environment shown in FIG. 5 could be the typical 802.11 network. In case of the network shown in FIG. 5, when a station (STA, WLAN UE) performs passive scanning to receive beacon packets, the STA receives the beacon packets from two or more APs which belong to a single AN. If the APs transmit the beacon packets to the STA, wherein the beacon packets include information of subscription service provider network (or AN) belonging to the AP, the STA can combine two or more packets with one another.
3. Wireless LAN and 3GPP Interworking
Interworking between wireless LAN and cellular network (3GPP) is divided into a scanning procedure for discovery of a wireless LAN network, an authentication procedure with the wireless LAN network, a cellular network discovery procedure, and an authentication procedure with a cellular network. A cellular network discovery and selection procedure is performed as a part of the authentication procedure with the cellular network.
3.1 Wireless LAN Network Scanning Procedure
The wireless LAN is provided with a name of a wireless LAN network as an SSID information element. A wireless LAN user equipment (WLAN UE) detects available wireless networks through the scanning procedure. The scanning procedure is classified into the following two types:
i) passive scanning which is a method of acquiring information by receiving beacons broadcasted from a network; and
ii) active scanning which is a method of acquiring desired information of the wireless LAN user equipment by requesting a network to provide the desired information.
3.2 Authentication Procedure with Wireless LAN Network
This authentication procedure is performed through an authentication management frame. In case of an AP and a wireless user equipment, which support 802.11i, 802.1x based authentication is additionally performed after an association procedure is performed.
3.3 Cellular Network Discovery Procedure
The cellular network discovery procedure is performed between a wireless LAN user equipment (WLAN UE) and a local authentication, authorization and accounting (AAA) server to provide ‘a supported public land mobile network (PLMN) list’ to the wireless LAN user equipment, wherein the PLMN list is required to perform a passive selection procedure.
3.4 Cellular Network Authentication Procedure
Authentication with a cellular network is classified into an extensible authentication protocol-authentication and key agreement (EAP-AKA) mode and an extensible authentication protocol-subscriber identity module (EAP-SIM) mode depending on an extensible authentication protocol (EAP) which is supported.
FIG. 6 illustrates an example of a related art interworking procedure between a wireless LAN and 3GPP. In other words, FIG. 6 illustrates an example of an interworking procedure between a wireless LAN and a cellular communication network. The wireless LAN system can interwork with a cellular communication network (for example, 3GPP2) in addition to 3GPP. The wireless LAN user equipment performs passive scanning (S601) or active scanning (S602, S603) to discover a wireless LAN network. The wireless LAN user equipment selects a wireless LAN network depending on the result of scanning (S604). A distribution service should identify through which AP a specific user equipment can access in order to forward messages within a distribution system (DS), and this is performed as an association procedure (S605, S606). There may be various authentication methods in allowing a wireless LAN user equipment to perform authentication with a wireless LAN network. In this embodiment, examples of the authentication methods include an open system authentication method (S607, S608) and a shared key authentication method (S609 to S612). The wireless user equipment performs authentication procedures (S613 to S623) with 3GPP network to use the 3GPP network through the wireless LAN network. In this embodiment, a wireless user equipment and a communication network support EAP-SIM.
4. Method of Forwarding Interworking Information
Examples of a method of forwarding interworking information of a network, which is interworking with a wireless LAN network, in the wireless LAN network include a broadcast method of interworking information through a beacon and a probe response method of an AP to a probe request of a wireless user equipment.
4.1 Broadcast Method of Interworking Information Through Beacon
Hereinafter, a related art beacon which is divided into two types using a concept called a layered beacon will be described. In other words, the beacon is divided into a network maintenance beacon (NMB) which is conventionally used and a network discovery beacon which includes the interworking information.
Network Maintenance Beacon (NMB) indicates related art beacon message.
Network Discovery Beacon (NDB) indicates beacon message which additionally includes the interworking information in addition to the related art NMB.
4.2 Probe Response Method of an AP to a Probe Request of a Wireless User Equipment.
The wireless LAN user equipment (WLAN UE) requests the wireless LAN network to provide the interworking information through a probe request message if it does not receive the NDB. The wireless LAN network immediately forwards the interworking information to the wireless LAN user equipment through a probe response message if it has the interworking information. Also, the wireless LAN network acquires the interworking information from a network, which is interworking with the wireless LAN network, through a given procedure if it does not have the interworking information.
FIG. 7 illustrates a series of procedures of requesting and acquiring interworking information in a wireless LAN user equipment in accordance with the related art. The wireless LAN user equipment requests the AP to provide the interworking information IE1, IE2, . . . through the probe request message (S710). If the AP cannot provide the interworking information, the AP forwards the probe response message to the wireless LAN user equipment, wherein the probe response message includes information (ComeBackDelay) as to when to retransmit the interworking information and ID (Query ID) for identifying request of the interworking information (S720). The AP acquires the interworking information, which is requested from the user equipment, from the interworking network (S730, S740). The wireless LAN user equipment sends the probe request message at a scheduled comeback time, i.e., retransmission time (ComeBackDelay) of the interworking information. At this time, the wireless LAN user equipment requests the probe request along with the query ID received through the step S720 (S750). Accordingly, there is no need to indicate the interworking information again. The AP transmits the information acquired from the interworking network to the wireless LAN user equipment (S760).
FIG. 8 illustrates an example of a method for periodically transmitting NMB and NDB. The AP determines what time the NDB will be transmitted and transmits the NDB timely. Referring to FIG. 8, it is supposed that a transmission period of the NDB is 4, and the NDB is transmitted per fourth beacon.
FIG. 9 is a flow chart illustrating a method for performing communication between two APs through a DS. The two APs are connected with each other through a single DS. Referring to FIG. 9, each AP includes a MAC layer management entity (MLME) and an RRB. The wireless user equipment STA transmits an action frame to the current AP (S901). The current AP encapsulates the action frame in a remote request frame, sets a destination address of Ethernet frame as a target TAP address (AP address to which the action frame should be transmitted) referring to the target TAP address included in the action frame, and transmits the destination address (S902). The target TAP receives the remote request frame and decapsulates the action frame (FT action request) encapsulated in the remote request frame, and forwards the decapsulated action frame to a required place. The procedure of transmitting the decapsulated action frame to the required place is apparent to those skilled in the art and thus will not be described. The target TAP transmits a response message. In other words, to transmit the response message to the wireless user equipment STA through the DS, the target TAP encapsulates a desired action frame (FT action response) in a remote response frame and then transmits the encapsulated action frame to the current AP, i.e., the AP which has transmitted the remote request frame (S903). The current AP which has received the remote response frame decapsulates the encapsulated action frame to obtain the action frame and transmits the obtained action frame to the wireless user equipment STA through wireless communication.
The wireless user equipment STA can additionally transmit the action frame to the current AP (S905), and the procedure of additionally transmitting the action frame to the current AP corresponds to the above step S901. The current AP can encapsulate the action frame and transmit the encapsulated action frame to the target TAP (S906). Also, the current AP can decapsulate the encapsulated action frame by receiving the response message to the encapsulated action frame (S907). These procedures correspond to the steps S902 and S903. Also, the current AP can transmit the decapsulated action frame to the wireless user equipment STA (S908).
The aforementioned related art has several problems.
First, the related art has considered that the current AP acquires the interworking information and forwards the interworking information to the wireless user equipment STA. In other words, each AP has acquired the interworking information requested from the wireless user equipment STA through an arbitrary entity of a network having the interworking information and an arbitrary method that cannot be defined. In this case, a problem occurs in that processing throughput of data to be processed by the AP increases.
Second, although the wireless LAN user equipment requests the interworking information, if the AP does not have the interworking information, the AP reports ComeBackDelay to the wireless LAN user equipment and tries to acquire the interworking information. In this case, the wireless LAN user equipment should forward the request message to the AP again to receive the requested interworking information after the lapse of time as much as ComeBackDelay. For this reason, a problem occurs in that the wireless LAN user equipment and the AP should transmit and receive a large number of messages to and from each other.
Finally, the wireless LAN user equipment should receive the NDB to acquire the interworking information from the AP. In this case, a problem occurs in that the wireless LAN user equipment transmits the probe request message of the interworking information as it does not exactly know a transmission timing point of the NDB.